The present invention relates to digital watermarks, and is particularly illustrated with reference to fragile and low-visibility watermarks.
It""s not as easy to spot a pirate as it used to be. The first time you laid eyes on Captain Hook you knew that you were dealing with a pirate. Maybe it was the black flag. Maybe it was his motley crew. Now times have changed. Today pirates wear finely tailored suits. Or they lurk in homemade manufacturing facilities in their garage. Yet a common thread binds today""s pirates to their historic comradesxe2x80x94they seek to profit from other people""s work and creativity. They remain common thieves.
Consumers increasingly face the difficult task of discerning genuine products from counterfeits and pirated copies. Pirates (including counterfeiters) annually rob industry in the order of hundreds of billions. Targeted items include banknotes, stock certificates, product tags and labels, artwork, images, music, videos, CDs, DVDs, etc., etc.
A solution is needed to effectively combat piracy and counterfeits.
Digital watermarking offers such a solution. Digital watermarking technology, a form of steganography, encompasses a great variety of techniques by which plural bits of digital data are hidden in some other object, preferably without leaving human-apparent evidence of alteration.
Digital watermarking may be used to modify media content to embed a machine-readable code into the media content. The media may be modified such that the embedded code is imperceptible or nearly imperceptible to the user, yet may be detected through an automated detection process.
Most commonly, digital watermarking is applied to media signals such as images, audio, and video signals. However, it may also be applied to other types of media, including documents (e.g., through line, word or character shifting, through texturing, graphics, or backgrounds, etc.), software, multi-dimensional graphics models, and surface textures of objects, etc.
There are many processes by which media can be processed to encode a digital watermark. Some techniques employ very subtle printing, e.g., of fine lines or dots, which has the effect slightly tinting the media (e.g., a white media can be given a lightish-green cast). To the human observer the tinting appears uniform. Computer analyses of scan data from the media, however, reveals slight localized changes, permitting a multi-bit watermark payload to be discerned. Such printing can be by ink jet, dry offset, wet offset, xerography, etc. Other techniques vary the luminance or gain values in a signal to embed a message signal. The literature is full of other well-known digital watermarking techniques.
The encoding of a document can encompass artwork or printing on the document, the document""s background, a laminate layer applied to the document, surface texture, etc. If a photograph or image is present, it too can be encoded.
Digital watermarking systems typically have two primary components: an embedding component that embeds the watermark in the media content, and a reading component that detects and reads the embedded watermark. The embedding component embeds a watermark pattern by altering data samples of the media content. The reading component analyzes content to detect whether a watermark pattern is present. In applications where the watermark encodes information, the reading component extracts this information from the detected watermark. Previously mentioned U.S. patent application Ser. No. 09/503,881, filed Feb. 14, 2000, discloses various encoding and decoding techniques. U.S. Pat. Nos. 5,862,260 and 6,122,403 disclose still others.
One form of digital watermarks is a so-called xe2x80x9cfragilexe2x80x9d watermark. A fragile watermark is designed to be lost, or to degrade predictably, when the data set into which it is embedded is processed in some manner, such as signal processing, compression scanning/printing, etc. A watermark may be made fragile in numerous ways. One form of fragility relies on low watermark amplitude. That is, the strength of the watermark is only marginally above the minimum needed for detection. If any significant fraction of the signal is lost, as typically occurs in photocopying operations, the watermark becomes unreadable. Another form of fragility relies on the watermark""s frequency spectrum. High frequencies are typically attenuated in the various sampling operations associated with digital scanning and printing. Even a high amplitude watermark signal can be significantly impaired, and rendered unreadable, by such photocopying operations. (Fragile watermark technology and various applications of such are even further disclosed, e.g., in assignee""s U.S. patent application Ser. Nos. 09/234,780, 09/433,104, 09/498,223, 60/198,138, 09/562,516, 09/567,405, 09/625,577, 09/645,779, and 60/232,163.).
Digital watermarking applications are not limited to counterfeit deterrence. Digital watermarking techniques are used in countless areas such as inventory management, content marking, serialization, indexing, internet navigation, tracking, linking, etc. Of course there are many other suitable applications.
The present invention provides an out-of-phase digital watermark. The out-of-phase watermark includes at least a first component and a second component. The second component is embedded so as to be out-of-phase with respect to the first component. In one embodiment, the first component is printed with a first ultraviolet (UV) ink and the second component is printed with a second UV ink. The first UV ink preferably has a shorter decay time in comparison to the second UV ink. The out-of-phase watermark has low visibility properties since, under steady-state UV illumination, the illuminating properties of the first and second watermark components cancel each other out. Other embodiments involve unique detection methods for a UV out-of-phase digital watermark.